United States
Department of
Agriculture
Forest Service
Pacific Southwest
Forest and Range
Experiment Station
Dwarf Mistletoe in Red and White Firs
in California 23 to 28 Years after Inoculation
John R. Parmebr9Jr.
Robert F- Scharpf
P.O. Box 245
Berkeley
California 94701
Research Note
PSW-406
June 1989
warf mistletoes are widespread in
California fir stands. Losses, including reductions in growth and
wood quality, predisposition to bark
beetles, and damage by secondary decays
and cankers, are mainly functions of the
numbers of infections and their distribution
in tree crowns. We have followed the dynamics of dwarf mistletoe populations in
inoculated firs since 1958,1-2when we began inoculations with Arceuthobium abietinum Engelm. ex Munz on young red firs
(Abies mgnifica A. Murr.) and white firs
(A. concolor [Gord. & Glendl.] Lindl.) in
the Sierra Nevada and southern Cascades.
This note provides an update of population trends in these trees from 1977 to 1986,
with data on additional trees, tree-to-tree
spread, changes in dwarf mistletoe ratings,
and rate of dieback of infected branches.
Parmeter, John R., Jr.; Scharpf, Robert F. 1989.
Dwarf mbtletoe in r e d a d whitefirs in Californ k - 2 3 to 28 years a$er inoculation. Res.
Note PSW-4%. Berkeley, CA: Pacific Southwest Forest and Range Experiment Station,
Forest Service, U.S. Department of Agriculture; 5 p.
Spread and buildup of dwarf mistletoe, Arceuthobiwn nbietinum, was studied on inoculated
white fir, Abies concolor,and red fu,A. mgn1j7ca,
in northern Califomia for 23 to 28 years. At the end
of these studies (1986). and in the absence of
overstory infection, 13 of 23 trees had dwarf
mistletoe populations that were the same or
smaller than the original populations resulting
from inoculation. Mortality of infections was the
main factor limiting population increases. Live
crown ratio of all trees averaged over 0.8. The
average ratio of tree height growth to vertical
spread rate of dwarf mistletoe was 11.5 to 1 in
white fir and 7 to 1 in red fu in the Sierra Nevada.
In the southem Cascades,the average ratio was 1.7
to 1 in red fir.About onefourth of thetrees became
infected in thebole. Of 14additionaltrees infected
by lateral spread of the parasite, 13 were within 6
m of the source of infection. Evidence continues
to indicate that losses from dwarf mistletoes will
be small in well-managed young fu stands free
from infected overstory trees and properly spaced
to promote good growth.
Retrieval Terms: dwarf mistletoe, population dynamics, epidemiology, vertical spread, red fir,
white fir, Abies concolor, Abies tnagnifica, Arceuthobiwn abietinm, Viscocea, Califomia
METHODS
,
Five red firs at Latour State Forest near
Mt. Lassen in the southern Cascades and 13
red firs and 11 white firs on the Stanislaus
National Forest in the central SierraNevada
were ~tudied.~'All trees were less than 10
m tall at the time of inoculation, had
branches to within 1 m or less of theground,
and were in areas free from natural infestation by dwarf mistletoe. Thus, these trees
were suitablefor studying population buildup, rate of change in dwarf mistletoe rating,
and distance of vertical and horizontal
spread.
The rest trees were inoculated by one of
1
three methods with freshly collected, local
sources of dwarf mistletoe: (a) in 1960,
clumps of fruiting dwarf mistletoes were
shaken near trees, approximating natural
seed discharge and deposition, (b) in-1958
and 1961, freshly discharged seeds were
collected and placed individually on
branches? and (c) in 1963-1967, freshly
collected seeds were soaked in water and
then placed individually on branches.'
Initially, the inoculated trees were monitored for mistletoe seed germination, penetration, infection, shoot development, h i t
production, and seed dispersal? After these
early observations, some trees were examined annually for new infections, shoot and
fruit development,and death of infection^.^
For other trees, time and travel constraints
precluded annual monitoring of populations and at times data only on tree height,
crown length, and highest infection in the
crown were taken. Periodically, detailed
mistletoe population data were obtained for
all trees. Thus, dates of data collection and
kinds and amounts of data varied from tree
to tree and from year to year and are specified for each factor discussqi.
Initially, for most trees, the infections
resulting from inoculation and subsequent
secondary infections were individually
identified with metal tags wired to
branches. As numbers of infections increased, this method eventually became too
cumbersome and time-consuming.Vandals
removed some or all tags from some trees,
and other tags were lost for unknown reasons. One red fir was cut, apparently for a
I
USDA Forest Service Res. Note PSW-405. 1989.
Christmas Wee. At different times, tagging
was discontinued, and numbers of live infections were recorded for each branch at
each branch whorl. Tagging individual
dwarf mistleloe infections wrmitted development of life tables. Counting live infections on branches by whorl provided data on
net changes in live populations and their
dishbution in tree crowns.
As dwarf mistletoe populations increased, the intensity of infection within the
tree was detemined by the 6-class dwarf
mistletoe rating system.5 For the lower,
middle, and upperportionsof the living tree
crown, the mistletoe in each was rated as
absent (0); light-less
than half the
branches infected (1); or heavy-more than
half the branches infected (2). The sum of
the numbers is the dwarf mistletoe rating
(DMR). Trees with 1 to 3 ratings were
considered lightly infected, trees with 4 to 6
ratings, heavily infected.
Tree and branch heights were measured
to 7 m with a telescoping, calibrated pole.
Beyond 7 m, heights were determined with
a clinometer. Dwarf mistletoe infections in
upper crowns were detected by climbing
trees with a 24-foot (7.3-m) extension ladder or by inspecting carefully with field
glasses.
RESULTS
Table I--Idumber of live kfecfionr in 1986 in trees irrocdated between 1958 and 1967
1
I
I/
1
1
Host
White fir
Red fir
I
Year
inoculated
1
Trees
1
Initial
infections
1
Live infections
1971 1 I976 1 1981 1 1986
Stanislaus National Forest
1960
1961
1963-67
I1
2
3
6
3
13
111
7
6
82
1
25
133
0
22
129
0
23
96
905
667
1
1
Latour State Forest
1958
5
28
596
lone tree, cut by vandals in 1978,had only a single infection that produced shoots
only twice and never fruited.
'No data recorded.
1
I
Table 2--Cwnulative mortality to 1986 of cohorts of dwarf mistletoe
infections detected and tagged at different tinzes
Interval of
observation
Host
Infections
Alive
in 1986
Moitality
Pct
Stanislaus National Forest
White fir
I Red fir
1
1
1I
I Red fir
1964-67
1968-71
1972-76
37
57
62
10
8
10
73
86
84
1964-67
40
6
85
Latour State Forest
I
16
Population Builldup and Decline
223
On the Stanislaus National Forest, popu731
lation changes were variable and inconsistent among 11white firs and 12red firs over
the 19 to 26 years since inoculation (table rional Forest. From 28 initial infections,she from first detection (table 2). Surviving
I). Mistletoe fruit and seeds were produced population increased to 905 (about 32 infections were generally on the bole or on
on all but 2 trees, both red firs with single, times) in 1981 and then declined to 667 main branch axes. Since inoculations often
male infections. By 1986, the number of (about 24 times) in 1986.
involved placing seeds on main branch
Population data alone do not indicate the axes, survival of early cohorts of infection
infections had declined in nine white firs
and three red firs, was unchanged in one red rate of new infections,but rather the balance was slightly higher, likely because later
fir, and had increased in three white and six between new infections and mortality of cohorts resulted from natural infections
red firs. One red fir with a single, male older ones. For four white firs and four red occurring mainly on secondary, tertiary,
infection was cut by vandals. Among the 13 firs on the Stanislaus, we have yearly data and quaternary branchlets. Among tagged
trees with static or decliningpopulations, all from 1976 to 1986 on the survival of all infections recorded from 1964 to 1976 on
infections had died on three trees, and only infections arising from inoculation. By 10 white and 15 red firs for which data on
one infection was still alive on each of five 1986, only 28 (22 percent) of the original branch rank were available, mortality for
trees. Population increases on the other infections were alive, but the total numbers primary, secondary, and tertiary or quaternine trees ranged from less than two times to of live infections increased to 246, indicat- nary branches was, respectively, 48 perabout six times the original population. ing that the change from 1976 to 1986 re- cent, 66 percent, and 80 percent over the 4 to
Total populations on 23 trees increased sulted from 100 deaths and 218 new infec- 16 years (to 1980) in which such data were
Lakcen (fable 3).
from 301 to 716 (2.4 times) in 19-26 years. tions.
Mortality among 1326 infections on all
Much of the mortality of mistletoe infecOn Latour State Forest, dwarf mistletoe
intensified in all five red firs inoculated, and test trees during early population monitor- tions was due to death of branches, caused
the rates of population increase were much ing (1962-1976) ranged from 73 percent Lo mainly by the parasitic fungus Cytospora
more dramatic than on the Stanislaus Na- nearly 100 percent within 10 to 26 years abietis Sacc. and girdling by rodents.
2
1962-65
1966-68
1969-72
I
USDA Forest Service Res. Xote PSW-4%. 1989.
Tabla
d& by I 9 0
d i y e r e ~m h of braaches
Year
Species
mdd
1964-70
1971-76
04dwarf
l:tkloe
h f e c t b m f ~ 8 1recorded ow
R w M inffer:hmx
percent
d a d by 1980 am bmckes of a e m t r d s
Rkwy
Secondary ~ e d a r y ~ a t
I
I
NO. b"Cb
No. Pct
No.
Pet
1-42 49
69 33
179 88
264 53
123
172
96
76
1 Msnn height (m)
Iplfected (pct)
4.8
67
7.6
38
7.0
18
8.1
7
11.51
0
lSpmd periods ranged f m 23 to 28 years from inmlrarim.
five branch m r k r l i 9 to 1986 at w r i o u periOCBT afier defection
of fist mi~fiefmi ~ f e c t i ~ w
spread in&cat& m avemge mnud rate of
spread of 2.6 em (rmge of -35.0 to 7.7 ern).
Average mnud gowlh in wee height for the
m e period (23 to 26 yr) was 30 cm, giving
an averageratio of height p w l h to veAcal
anisdew spread of 11.5: 1. lFor the 12 red
fks, vertical misdetor, spread averaged 4.5
cnnlyea (range of -2.2 eo 18.0 cm) and epee
height growth was 32 crnlyear (range 14-59
cm), giving arstrio of tree gowlh to vertical
misfleloe spread of 7: 1. For the five red firs
at the Latow Slate rest, average mistlew
verticd spread over 28 years was 20.0 cm/
year (rmge 13 to 24 cm). Height growth
averaged 33 crn (range 25 eo 40 cm)/year,
giving a ratio of height growth to vertical
spread of 1.7:1.
averaged0.87 (range 0.75 eo 0.93) for white
f ~and
s 0.88 (range 0.78 to 0.95) for red firs.
Percent of live crown i n f x t d averaged 15
(rmge 0 to 47) for white firs and 27 (rmge Bole Infections
0 to 45) for red firs. Two red firs with single,
Two bole irmfections result& from inocumale ide~rionswere considered to be min- lations, and 15 resulted from s e c o n w
fwted, since misfleloe reproduction was idecdons within inoculated trees or from
precludd. The DMR averagd 1.5 (rmge 0 spread t~ smomding trees. Excluding the
to 3) f a white f i s md 2.0 (range 1 to 3) for two f m inoculations, bole infeeions derred firs. Combin& raring for the 20 trees veloped in 10 (24 percent) of 42 trees. Bole
was 1.8. In none of these e e s was the upper infecdons sccwed mainly from brmch
third of the crown infaed, md only seven infec~onsgrowing into the bole, but some
had infwlions in the middle third.
were from direct infection of young needleAt Earour after 28 years, K R of five red
ng main stems.
fus averaged 0.79 (rmge 0.61 to 0.92).
Percent of live crown infect& averaged 43 Tree-to-Tree Spread
( m g e 0 to 70). The ""O" value is an miface
Because inoculated trees were in isolated
owing to the fact &at the highest infected areas free of natural infwlion, spread of
b m c h was also the lowest live brarrch in misdetm to surrounding trees could be
Dwarf Mlstletw Rating (DMR)
one tree. The avemge dwarE rnisdetw rat- monieorec9. Inocuhred trees separated by
On the S m k h u s N a ~ o n dForese, rm- ing was 3.0 (range 1 to 5).
less than 3 m from one another were considor& of cmwn lengLks, md lmabon of inered single loci of infecrion. Inoculated
fated b m c k s p r n i u d de~miimbonof Vertical Spread in Relation to Tree
vees in which misdems never hired were
live crown ratios (LCR), percent of live Height Gro*
not included. By Ekes criteria, 14 loci of
c m m iinfectd, md D m for 10 white and
On the Smislaus Nadond Forest, the infecrion were identified. The rate of infec1 0 r d h ( 3&~haadcukork&enLspsmd rate of vertical spread through me crowns lion decreased with dismce from see64
we= not incluw). AhougR live cmwns was delemined for 11 white firs and 12red souxe (rQble5).Of the 14 srces h a t k m e
were not m w w d at the t h e d imuh- fis. I;of white fis, the d s m c e fmm the infect&, 13 (93p x e n t ) were within 4 m of
don, only trees with LC23 of 0.8 or more highest b m c h infmed by inmulaeiclw to %mi.One of 14 gees ktween 6 to 8 rn and
werp: wed. After 2% to 26 y m , Em the highest b m c h i n f x t d by s e c o n w now of 13tmes &ween 8 to 10rn fmm loci
Lower uninfecM and h f w a branches
a h died as bey k c m e shd& md
physiologidly weaker as h e trees grew in
heighb. Why hfecM bmchbls died, thus
mling h&viduah irmfa~ons.In lime, entire
bmches died (fcmble41,$iilfingdl hfections
on the b m h . 144s expxted, the longer a
bmch was infwted, the more l&ely it was
to die. Over M o f the bmches infected for
more &m 16 t~ 18 yeas were dead. T r e s
at Latour were not monibsd regul~ly
emugh to pmGde conskknt reor& on
date of h i g d infm~on of h c h dm&,
but for h e e mas, h e con&bon of dl
bmches less than 3 m from the pound was
r ~ o r MThere
.
were 133 live b m h e s in
1968,40 in 4978,7 in 4981, and none in
1986.
a M ~ olocus,
d but the new Uwtions &&
out and q m d was PBjsmfm m ~ d
mmm.
DISCUSSION
R ~ o m e n w o n for
s m m @ g red or
WGEf i sm&
~
hfe~t&
with dwarf x&&tm b ~ l ~ sd te~ ~ 3a- ~b l~k~h e n oft repducfion h idestd s m & , clmutfing
foHow& by plm&g or natural regenera-
of h f e ~ o nin me fus are crown mdos (0.61to 1.O)mdlight Life~dcfi
Iowe2
23 inmnkM trees on the ratings (1 to 3) grew $itelk d & r r e l e s ~ ,
S d & n s N & d Fore& mistletoe p p n - None of om trees had a live crown ratio
below 0.61,and only 5 (20percart) fad
ratios below 0.81. fistlebx ratk~gs\veae
d
light in 96 percent of & I em9 and hem-7in
es@b&&-9bb ppula~onsa p p ~ e n a y only 4 peecent.. Since most wes hati g c d
light infixtion 1eveis,
bw mks of infection, even when live crown ratios ad.
my damage. caused by rnis~emwill 'be
are p d u c d for sevend y w s .
Death of infections generally involved srndl.
Bole infections develodd in only 2
.4 s r death of bmchm orb m h l e from
~ one or
idly rodent chewing cent d the trees. Since such iwfecuons do
a d bmch gb&hg by s ~ m fungi
m and not appear tocause much h x a g e in young,
i
Smdl secondary
ter~ia~njfast-gowingFirs? ,sSignificmtbmage is not
bmcMe& sa~smaywere more liable to expet&.
Tnere was some bkerd spread sfmis9edie from gbdhg, hence the higher percent
of early. deaths mong infections on these toe to firs adjacent &e test trees, but
abut. 4 m 6 m
higher bmch ranks. B e a u s many of the almost di spread was -*vittt-%
on these branches produce very after 23 to 228 yws, Zlerefore, h e spread
and have Btde effect on the tree, mong f k s in tfls stud.] -+/asslightly kss
their loss is s f litrkepnsachd h p m c e . In dhan the average of a b u t 09 ft (0.2'7 m:
n which brmeha b a m e heavily in- lateral spread per yeax reported for ponderdm! of entire bmsches was fie- 0% pine in the wutbwest?
re$&@provide furtiler evidence
quent and often led to eliminadon ass" large
shouldbe
numkm of idmdons and to marked de- that 10sses from dv~&mi~tle~w,s
cline inmisdetm ppulafions, On h e most smdl in wdl-mmagd young sands free a l
If care i s taken to eeErnlheavily i d a t & red firs at bmw, virtually infectedoa~erstwy,
nate overstoq sources s f infw~~oc
and
aof brmches less M "4 mom
ground have died.
s m d s are spaced pfoperEy to pro~ob:g d
V e d d spread on the S B ~ S ~contin~ U S growth, scattered idectmns withha young
ued to lag v~el:%l
b h b d height growth in the fii stands snould not affect prcxjcctiia~ty
29 trees studied. By 1986,ratios of height appreciably.
g~owthto vertical mistletoe spread for red
how q i d y dwdrnisaem might i n a s e
in y m g s m & with satkred iwfeM
. Such i n f m a ~ o nnl ~ m a e l yq u h e s
%mg-m
W P Q ~ @ ~
of&p1w
;
u*&
ZId
refine data.
h & hresults from &me studies in&of MBdup md spread
f yowg firs were. dow."z7
FuPghemo~,ow rmbnlts &ow aihst after
a b u t 2 d&es sf iniM i n a w s , dwarf
misdem p s s p h ~ o mhave begun to level
off or d61he i
n the E w mder study. For
empBe, for the heow red fm, SmkBZpw
red fis, and Smslms white fm, 19%
ppul&ons of live infmbms w
fmmd w h i k f ~were'7to
s
1 md 151.5 m 11,
cmk 96 percent, md 79 percent,
r a p ~ v e l yThese
.
ratios represent a slight
i n c r in
~ the vemcd spread rate for red
fm and a sEghe decrease in spread rate for
enaces in sumpGblity mowg em in &f- white fm since ow ea11ier ~pfi."us*
ferent arm (or aferent micmgma~c newly dB the trees on &e Sm~slausNacm&dom in &ffe=wt ikaw &at influeme t h n d Forest continue to outgow the up
w& ~qpeadof the
ite by a wide mamisdew
md (3) rate of death of @.
id^& b
S.
At h m w 9 werage rates of vertical
We have p~~owstlgr
on differ- spread in red firs were gaiter (20.0 cm/
ences in p p ~ b ~ do n
p
d w d m k - yaw) by 1986 than hey were in 1976 (7.3
d e w at the mo Fmesksksl
Ow idmbon data cww),but 'the rate of host height gowh9
in &at r e p a b&mM that the dfferencw (avg, 33 crn&es) still exceded the rate of
were due in part to h e shorter incubahon ver%cdmisdem qr@d by a ratio of 1.7: 1,
period, for dwarf mkdew plants at l h b ~ g 8 . ~With the dminkhing d dwarf misdetm
Higher inhid rates of ~ m d o n
following p p l a h m s during the h e sever& yaws, it
imuhbali (28 p m n t ) were Jm noted on is 1ie1y
$pee height growth will conredfm at htowPbut not onwhite fm? The thm tooutpace vedcd s p d , and b a t h e
are
ut. they might involve e w h n nces, p v e m g e Ufermca
in w q ~ b & eorSY
mong
pop&
C k r =d&
h&mk
a
sp G c a l y
ge and grow& 10s &om dwuf
misaew in firs me relami to live crown
ratios and m the mount of live crown infectais s has beaq r e p d by Sckrpf'?
S c m f f i n d that trees with g ~ live
d
END NOTES AND BL5ZZENCES
'%&serpf, Robert P.;Pameter, J&n R., Jr. 1976.
Popddion btdild~p and vertical s p r a d of d i v e
wisthros an young red d white *firsin Cal$iornia.
Res. Paper PSW-HZ. Be&eHey$I,
CA:Wcfic Southweat Fomst
Rang2 E x p ~ h e n Station,
t
Forest
Sewice, US.Department of Aghcdturn; 9 p.
SWarpf,Ro2wflP.;Pame%:, J.R., Jr. 1982.Pop&-
kpt~rtrnmtd Psgrialtmr; 9p.
JS&i?rpf,R.F.;Pis,mWkrsZ.R., Jr. 1%7. Tke bblogj a d @hilogy ofdv"&~gr~ktietes
Arceuthabium
~ a m p j j I o p A mf. babiekmm~p ~ m i t i z k gtrwji51s i i ~
Cali,fornh.Tech. Bull, 1362.WssS.hg?nn,E:
Fore8
Sewice, U.S. D~p~rtnne~a
of jL%gricu&tam;
42 p.
4S&apfs Robert F.; Pameter, LR.,4a. 1952. T k
eollec~ba,storage, a d g e r ~ & w % bqa
n SLC~S oj a
dwr-fd-t~~soe.
Journal of Fomrtxry GO(8). 551-552.
*H~aspdksisl&h* Fr& 0.1977. Tbs 5 - c h s dvwf
w&t6etoe ratiag system. C h . Tech. Rep. RM-48. P e t
&Em, 03 Rocky h4hquh F a s t and Rang8
a t S~icm*Fomst Sewiicx* U.S. Dqmrbnmt
d Ag~dgasm;
7 p.
%SSarpfOR&ri P. I&. &wagmistletoe om rsd
fir...i@ectim. ard eo?Jrol im twsrstory &zP&.
We.
USDA Fmae SineiceRa.Note P5W424. 1989.
B & a p f e Robert. P. 1969. &Dw$mbIl~boc on red
@r...ifecIk O P control
~
ia d r s t o r y sIQ&. R a .
Paper RSW-50. Berkeley, @A: PaciF~ck u h w e s r
F m s t and Range E~rirnmt
&ion, Eiomt Service,
U.S. w m m e of Agricdmm; 8 p.
'S&arpf, R&rt 6;. 1979.h@htZe~m-i@ec8edB
r e t i p : growth afier release. Res. P a p r BW-143.
Be&eley, CA: P a S i c
e a Fomst md Wmge
' P m e k ~ ,J& R., Jr.; &hWpf, Ro$cJfi F. 1982.
S6em infictiorn by dwarf m&tletcie in CaliJCOr~k
fi.
Res. Paper PSW-165. Berkeley, @A: Pacific Souehwest %rest 4 Rmge E x p h e n t Station, Fom81
Service, U.S. k p a m e n t of A g ~ c d m m 7; p.
%~lrrwkswo&, P&
6.1961. D w o $ ~ d l e i mO I
~ ~ O ~ F &)k
O S b
O8 i
k ~0~lh~13.96.
Tech. Bd. 1246.
Washings, LC: Forest Sewice, U.S.k p m m t of
A g ~ c d m %~12
; p.
The Authors:
JOHN
pARMmER9 JRe ~ m f e g r of
~ r~ h m
pathology, Univamity of California, Berkeley.
ROBERT ni: S C W R W is p m j a l e d e r - f ~ m e t
dime
wiphbdoduammin B e k e l e ~ .
of A g r i d m ~9; p.
Pmms of m y race, color, national origins, sex, a p . religion, oz with my handicapping mditions
are w d m s to we m d enjoy dl fwilitiea, p g m r , md services of the U.S. w a m e n t of
Agricdtum. Dircrirnkatim in m y fown is strictly against agency policy, and should be mp*d to
the S-~ary
of Agniculaum, WashiPlgm, DC 20250.
USDA Forest Service Res. Note PSW-406. 1989.